1. Field of the Invention
This invention relates to a continuous process of melting sponge iron in an elongated horizontal reactor, wherein sponge iron is charged onto the molten material in an intermediate region of the reactor, carbonacous fuel and high-oxygen gases are blown into the molten material, and slag and molten iron are tapped at opposite ends of the reactor.
2. Discussion of the Prior Art
The so-called direct reduction processes normally result in a product described as "sponge iron". It is produced from iron ore, from which only the combined oxygen of iron oxide is substantially removed with the aid of suitable reducing agents whereas the iron ore remains in solid state and its external shape is preserved.
The sponge iron produced from ores which have a sufficiently high iron content can be used directly as a substitute for scrap in the conventional steep production. In some cases, particularly if the sponge iron is fine-grained and must be transported and stored for a long time, the sponge iron is briquetted immediately after its production.
The electric arc furnace has proved to be particularly suitable for the processing of sponge iron to produce steel and is being used for that purpose throughout the world. But the electrical energy required for that purpose is expensive and often can be produced only with relatively high conversion losses. In addition, electrical energy is not available everywhere under acceptable conditions and in adequate quantities. For this reason a melting process in which primary energy source could be used directly would have considerable advantages.
A further disadvantage resides in the fact that the operation is discontinuous. This involves a higher consumption of energy and fluctuations of the rate and composition of the exhaust gas which is formed and which can be used for other purposes.
It has been proposed to melt sponge iron in a continuous operation in an elongated horizontal reactor (Journal of Metals, June 1969, pages 50 to 56). In that operation, the sponge iron is charged onto the molten material in an intermediate region. The intermediate region of the reactor is circular and preferably consists of an electric arc furnace because in that case the supply of heat and the required agitation of the molten material by inductive agitation can be controlled independently of one another, different from the use of burners. The carbon is preferably charged into the reactor as the surplus carbon which has been incorporated in the prereduced pellets. Alternatively, carbon may be separately blown into the melting zone. The circular melting zone is adjoined on one side by the refining zone and on the other side by the slag-purifying zone. In the refining zone, oxygen is blown on the molten material through lances. The exhaust gas from the reactor is reducing and for this reason is fed to the direct reduction unit for a utilization of its chemical reducing potential.
It is known from German No. 24 01 909 to blow fine-grained sponge iron, oxygen and fine-grained coal from below into molten material in a crucible-shape reactor in a continuous operation. The exhaust gas consists almost entirely of CO and after a collection of dust is used in part as reducing gas for a direct reduction in a fluidized bed, another part is recirculated to the reactor as a carrier gas for entraining the sponge iron and the coal, and a further part is afterburnt after a dust collection and used as a heat exchange fluid. That process can be used only to process fine-grained sponge iron and is combined with a direct reduction in a fluidized bed.
In a similar procedure known also from German No. 24 01 540, fine-grained sponge iron is blown into the molten material from below and sponge iron in the form of lumps or pellets is charged onto the surface of the molten material in the crucible-shaped reactor.
In both cases a recycling of the exhaust gas consisting almost entirely of CO into the molten material is required. That gas cannot be expected to have a reducing activity and it can be used substantially only as a carrier gas for entraining the coal and the fine-grained sponge iron, as a gas for protecting the blowing nozzles, and as a fluid for agitating the molten material. A disadvantage of that practice resides in that the gas must be purified, cooled and compressed before it is re-used. The cooled gas which has been recycled must be reheated by the molten material so that heat is extracted from the process.
It is an object of the invention to avoid the disadvantages of the known processes and particularly to permit a continuous melting of sponge iron having a large particle size range in an economical manner and with the aid of virtually only solid carbonaceous fuels.